Current sensors and current sensor controls are used for various purposes and take various forms. One common form of AC current sensing control utilizes a current transformer to develop a control voltage proportional to the electrical current passing through the sensed wire. Typically, the current transformer consists of a core or flux concentrator configured as a continuous band or closed loop, passing through a solenoidal coil. The magnetic field resulting from the current present in the wire or conductor to be sensed induces magnetic flux into the closed path of the flux concentrator. By transformer action, the ampere turns of the conductor are transformed into equivalent ampere turns in the linked solenoidal coil. The electromotive force (emf) so generated is conditioned and amplified as needed and may be used as a control voltage.
Current sensing controls are used for under and over current monitors as well as linear or proportional applications. In such monitoring applications, the resulting control voltage may only be required to provide an indication of the presence or absence of a critical current level. On the other hand, the control voltage provided by the current sensor may be used for various control functions which bear a linear, or at least proportional relation to the level of the sensed current. Current sensors are often employed in conjunction with electrical motors to provide an indication of the mechanical load on the motor by virtue of the sensed current level. One such example occurs with respect to motors used to drive compressors and/or fans in various refrigeration and heat pump systems.
A typical form of current sensor in accordance with the prior art has employed an annular solenoid coil in conjunction with a flux concentrator formed of two pieces. The solenoid coil is relatively bulky and expensive, particularly when used for those situations which require relatively low cost and/or compact design. Moreover, because of the relatively large number of turns in a conventional solenoidal coil, some variation in the actual number of turns from coil to coil typically exists, thereby giving rise to similar variations in the resulting signal. Similarly, such use of a solenoidal coil has typically required the utilization of a flux concentrator of two pieces to facilitate the mounting of the coil thereon.
Accordingly, it is an object of the present invention to provide an improved current sensor which is of relatively low cost to manufacture. Included within this object is a provision of such a current sensor which is relatively well suited for utilization in a system adapted to be mounted on a circuit board.
It is a further object of the present invention to provide an improved current sensor control which is capable of providing a reliable indication of the AC current within a conductor to be sensed.